Structural unit



p 1963 A. A. GAssNER ETAL 3,103,025

STRUCTURAL UNIT- 2 Sheets-Sheet 1 a QN OM. QN

Filed Dec. 3, 1958 VENTORS NER mm. KAHN IN A RED A.GASS

THEIR ATTORNEYS A. A. GASSNER ETAL 3,103,025

STRUCTURAL UNIT 2 Sheets-Sheet 2 INVENITORS ALFRED A. GASSN ER HARRY J.KAHN THEIR ATTORNEYS Sept. 10, 1963 Filed Dec. 3, 1958 United StatesPatent 3,163,025 STRUCTURAL UNIT Alfred A. Gassner, New York, and HarryJ. Hahn, Fresh Meadows, N.Y., assignors, by rncsne assignments, toKaiser Aluminum & Chemical Corporation, Oakland, fialiih, a corporationof Delaware Filed Dec. 3, 1958, Ser. No. 777,921 12 Claims. ill. 14-1)The present invention, generally, relates to improvements in structuralmembers and particularly to lightweight structures for forming bridges,derricks and the like, the elements of which can be prefabricatedreadily and transported for assembly at the site.

For bridges it is necessary to take into consideration the structuraldead-weight of the bridge itself in addition to the loads or stresses towhich it is subjected in determining its structure and safety factors. Alarge proportion of the load-carrying capacity of a bridge made ofstructural steel and concrete is used for supporting the dead weight ofthe bridge, and as the length and/ or Width of the bridge is increased,an even greater proportion of the load-carrying capacity'rnust beutilized to support the dead weight of the bridge. Moreover, inconventional steel bridges, each girder or beam must Withstand any loadapplied to it independently of the other beams, so that the size andstrength of the girders or beams is very great.

In accordance with the present invention, a load'carrying structure isformed of a relatively small number of easily prefabricated parts ofsuch weight and dimensions that they may be transported readily from aplace of fabrication for assembly at a site. A load-carrying structureproduced in accordance with the present invention includes a pluralityof hollow beams of generally triangular cross-section positioned side byside in a substantially parallel relationship with the apices facing inthe same direction. The corner pieces of adjacent beams are attached inan unique manner, which will be described in greater detail hereinafter,so that one side of each beam is disposed in a substantially parallelplane with a similarly disposed side of each other beam. A sheet orsheets of light-weight metal, such as aluminum or an aluminumbase alloy,join adjacent apices to strengthen and stiffen the structure anddistribute the stresses on the respective structural elements so thatthe load-carrying capacity of the structure is at least equal to that ofa conventionally constructed load-carrying structure of far greaterWeight. Inasmuch as sheet metal of the type indicated is capable ofwithstanding substantial compression or tension stresses when adequatelysupported against buckling, a very strong load-supporting structure ofrelatively light weight can be produced by using sheet metal incombination with the reinforcing elements at suitable locations.

A bridge constructed in accordance with the invention embodies asemi-monocoque structure in which the hollow triangular beams withstandthe various loads and stresses to which the bridge is subjected. Theupper sheet or sheets forming the top of the structure resistcompression stresses, and the sheet or sheets forming the under surfaceof the bridge resist tension stresses. Moreover, in such a bridge thearrangement of the elements is such that a load applied at any point issupported by all of the elements acting together as a unitary structure,thereby enabling lightweight metal to be used in the bridge with amarked reduction in dead weight without sacrificing strength.

A roadbed of, for example, reinforced concrete is formed directly on theupper surface of the semi-monocoque structure. Preferably, the roadbedis formed by pouring wet concrete over reinforcing members which includevarious structural members of the beams, to thereby 3,103,025 PatentedSept. 10, 1963 distribute the stresses relatively uniformlythroughout-the bridge structure.

Bridges and other structural members according to the invention have theadvantage over structural steel bridges of requiring little or nomaintenance other than keeping the roadbed thereon in repair. Paintingis reduced to a minimum, and little or no corrosion of the aluminumelements will take place under normal conditions of use. In thoselocalities where salt Water corrosion might occur the aluminumcomponents can be anodized to increase their corrosion resistance.

Inasmuch as the beams themselves are formed of lightweight metals suchas aluminum alloy, and these beams can be made in suitable lengths forassembly at the site, they can be prefabricated and transported readilyby means of trailers or the like to the construction site.

For a better understanding of the present invention, reference may behad to the accompanying drawings in which:

FIGURE 1 is a perspective view in partial section of a typical bridgeembodying the present invention;

FIGURE 2 is a view of a section of the bridge taken along the line 2-2in FIGURE 1;

FIGURE 3 is a View in partial cross-section taken along the line 33 inFIGURE 2; and

FIGURE 4 is a view in partial cross-section taken along the line 4-4- inFIGURE 2.

Referring to the bridge shown in the drawings as an illustrativeembodiment of the invention, the bridge 10 is 50 ft. long and isprovided with a 24 ft. wide roadbed 11 of cast concrete,part of which iscut away in FIG. 1 to reveal a network of reinforcing rods and the uppersurface of the structure. Each 50 ft. section of the bridge Weighs11,300 pounds, only a fraction over nine pounds per square foot, and thebridge has a load carrying capacity satisfying highway requirements of abridge of the size indicated. The arrangement of the various structuralmembers for the bridge takes into consideration the torque loadingsproduced by wind against the side of the bridge and loadings produced byvehicles crossing the bridge. In addition, the bridge has withstood inone test operation an eccentric loading of percent of the design momentplaced six feet from the center of the roadway.

Referring now to FIGS. 1 and 2, the bridge 10 is formed of three beams12, 13 and 14, each of which is of hollow triangular cross-sectionhaving an upwardly disposed base portion 15 and a downwardly disposedlower apex 16. Each of the beams is of isosceles or equilateraltriangular cross-section, each side of which is formed of sheets ofaluminum or aluminum alloy of appropriate thickness to present sides 17,18 and 19. The elongated relatively narrow load-bearing beams aredisposed in side-by-side and interconnected load-transferringrelationship.

As best. shown in FIG. 1, each of the sides 17, 18 and 19 is reinforcedby means of a plurality of aluminum angles 20 extending transversely ofthe beam. The angles are of a type commonly known as bulb angles; thatis, they have thickened and rounded outer edge portions 21, as shownmore particularly in FIG. 4. Moreover, the sides 17, 18 and 19 of eachbeam are reinforced by positioning these angles 20 at spaced-apartintervals along each beam to stiffen the sheets against lateral flexingand, thus, improve the resistance of the sheets to deflection undershearing stresses.

To reduce further flexing of the sheets, each beam is provided at itsends with channel members 26, 27 and 28 as seen in FIG. 2 and similarchannel members spaced therefrom and forming the ends of the beam unit,members 26a, 27a and 28a being visible in FIG. 1 and only member 28::being visible in dotted lines in FIG. 4. The

flange 45 is formed on the corner piece 4% lower ends of the channelmembers 27 and 28 are secured together by a gusset plate 29 in the formof an aluminum alloy angle. A gusset plate 39 (PEG. 4), similar to theplate 29, is used to secure the lower ends of the channel members 27aand 28a. The lower ends of the previously described angles which arespaced apart throughout the length of each beam are not securedtogether, except those at approximately five foot intervals.

All of the angles 20 and the end channel members 27 and 28 are securedat their lower ends to an apex corner piece 22 which extends over theentire length of each beam. As best shown in FIG. 2, the apex cornerpiece 22 of each beam is formed of an aluminum alloy extrusion having athickened Web or base portion 23 and outwardly diverging edge flanges24- and 25 to which the sheets forming the respective sides 13 and 19 ofthe beam are secured by means of rivets, bolts or the like, indicated bythe numeral 31. A side flange of each channel member 27 and 28 is alsosecured by means of the. rivets or bolts 31 to the flanges 24 and 25 ofthe apex corner piece 22.

Reinforcing plates 32 and 33 are secured to the outer surfaces of theflanges 24 and 25 by these same rivets or bolts 31 at each end of thebeams. Filler pieces 34 and 35 are inserted between the reinforcingplates 32 and 33 and the side sheets for sides 18 and 19 of therespective beams to provide a smooth joint and to further reinforce theapex 16 of the beam. The intermediate angles Zll are similarly joined tothe apex corner piece 22 but, as mentioned above, without the gussetplates except for those angles 20 at approximately every five feet alongthe length of each beam.

The two upper corners formed along the length of each beam by thechannel and angle members with the ends of the base 15 are reinforced ina different manner. As shown in FIG. 2, the corner piece 4% has a baseflange 4-1 which is inclined acutely with flange 42, the angle beingessentially complemental to the angle between the base 15 and the side19' of each triangular beam. The flanges 41 and 42 are riveted, orotherwise secured, to the aluminum sheets forming the sides l'i7 and 19and to the flanges of the channel members 26 and 28. An upwardlyextending and is inclined at an angle, as shown in FIG. 2. The upper end44 of the flange 43 is turned over to lie in substantially a horizontalplane, which will be referred to again presently. A ridge 45 extendsfrom the lower end of the flange 43 furtheumost from the flange 44.

A corner piece 56), formed on the adjacent triangular beam, has a baseflange 51 and a flange 52, both formed similarly as the flanges 41 and42 described above. An upwardly extending flange 53 is formed on thecorner piece and is inclined at an angle matching that of the upwardlyextending flange Ben the corner piece 4d. The upper end 54 of the flange53 is turned over to lie in in a substantially horizontal plane. Arecess 55 is formed at the opposite end of the flange 53 from theturned-over end 54, and it extends throughout the length of the cornerpiece 50 to receive the ridge 45 as shown in FIG. 2.

With the corner pieces ill and 5t? placed together, as shown in FIG. 2,it may be seen that a force applied in a vertical direction will beresisted by the inclined flanges 43 and 53. To secure these two cornerpieces 44 and 50 together more positively, a plurality of bolts 56 arepositioned at spaced-apart intervals along the entire length of thebeams.

The corner piece 69 along each side of the structure is formed somewhatsimilar to the corner pieces described above. That is, the corner piece60 is provided with a base flange 61 and a flange 62 inclined at anacute angle therewith. A channel member is supported in cantileverfashion between two flanges 64 and 65 extending from opposite end of anupwardly extending flange 66 of the corner piece 66). The channel memberas provides additional footage in the over-all width of the structure tosupport the roadbed 1-1.

As shown in FIGS. 1, 2 and 4, the apex corner pieces 3.6 of the hollowtriangular beams 12, 1.3 and 14 are joined by means of a sheet "Ill ofaluminum alloy to completely close the bottom of the bridge structure.The sheet ill, which may be either a single large sheet or a pluralityof smaller sheets, is reinforced at intervals by means of transversangle members 71 which may be substantially identical to the anglemembers 2i) including the bulb ends 21, FIG. 4. The longitudinal sidesof the sheet 7t"; are attached by means of rivets or the like to alongitudinally extending T-shaped angle '72. The T- shaped angle '72, inturn, is attached to the base flange 23 of the apex corner piece 22 bymeans of bolts 73, or the like. As shown in FIGS. 2 and 4, the anglemember 71 is secured to the base sheet 7e) by means of rivets 74 spacedat appropriate intervals along the length of the angle 71.

At spaced-apart intervals along the length of the bridge structure,concrete footings are provided to support the apex corner piece 16 asshown particularly in FIGS. 1, 2 and 4 of the drawings. A plate 81 ispositioned on each of the concrete footings Sll and is held in place bybolts 82. A recess or channel 83 in the upper surface of the plate 81 isadapted to receive a block of suitable resilient material 34, such asbronze impregnated with oil, on which rests a bearing plate 85. Anelongated bolt 36 is provided with an intermediate nut 87 to assist insecuring the plate 81 to the concrete footing S0, and the nut 83 at theupper end of the bolt 86 is tightened only sufliciently to maintain theupper plate in position. As it may now be seen, this type of bearingpermits longitudinal movement of the structure relative to the footings8%.

As described previously above, the upper corner pieces 4% and 6d areprovided with turned-over flanges 44 and 64. These flanges 44 and 6d areformed such that Z- shaped shear tie members or elements 9%) may beattached thereto by means of rivets or bolts 91 and are spaced atintervals along the length of the structure, as

est seen in FIG. 1, to increase the shear strength characteristics ofthe concrete roadbed 11.

The upper sheet for side 17 of each triangular beam supports a sheet 92which has transverse corrugations 93. The corrugations 93 are actuallyenclosed by and become part of the concrete roadbed 1]. to give theroadbed additional support between beam flanges. Of course, thecorrugations 93 may be longitudinal, if desired, in which case they alsoserve as compression material prior to the establishment of compositeaction-between aluminum and concrete.

The upper flanges of the respective Z-shaped shear elements 94} areused, for convenience, to support a network 95 of reinforcing rods.Portions of the concrete roadbed 11 are cut away in FIG. 1 to show thisnetwork of reinforcing rods being supported directly above the uppersurface of the bridge structure. The roadbed 11, new, is formed bycasting the wet concrete direotry on the upper surface, described above,of the structure. The concrete will flow between the transversecorrugations 93, as seen in FIG. 3 and, thus, will enclose the Z-shapedelements flfl and the network 95- of reinforcing rods. Thus, the sheartie members E i will become fully embedded within the road bed slab 11.In the finished permanent composite bridge structure suitable means suchas the sheets 7t) joining lower apices l6 and the downwardly inclinedsides T18 and 19 of the beams act as the primary tensile load-bearingelements of the structure while the road-bed slab acts as the primarycompression load-bearing element in the structure.

To further detail the illustrative bridge structure, all of the aluminumsections are formed of 606l-T6 aluminum alloy (an alloy composed of0.25% copper,

0.6% silicon, 1.0% magnesium, 0.25% chromium, and the remainderaluminum).

By utilizing the structural arrangement described indetail above, thealuminum is used to its greatest efficiency and, therefore, its cost isnot unnecessarily high. The cubic volume of concrete required for theroadbed is reduced by from one-third to one-half that customarily used,a factor which reduces still further the amount of dead weight to besupported by the beams. The concrete roadway 11 is formed integrallywith the upper structure of the bridge and, therefore, is supportedthroughout its area so that it will not crack under load. In addition, aload applied at any point on the structure will be supported by theentire structure and not merely the beams immediately beneath the load.That is, the entire bridge structure is deflected by a load appliedthereto. A structure as described above provides its greatest supportunder areas that will be highly loaded, and lesser support in lightlyloaded regions. The lightness of the structure lends itself to ease ofmobility by all means of transportation and reduces the requirement ofheavy field handling equipment.

A semi-monocoque cellular structure of the type described above hastremendous torsional rigidity to the extent that a load placedeccentrically on one side of the structure activates all of the materialof all the beams, requiring the entire structure to contributeresistance to the load and not solely the local beams adjacent to thepoint of load application. This alleviates the requirement for theconcrete roadway slab to act as the primary load transferring member.Actually, the centroid of the composite section is just a little belowthe lower surface of the concrete.

It will be understood that various dimensions of a structure for aparticular purpose may now be calculated by one skilled in the art usingthe structural arrangements described above, and more than threetriangular beams may be used in a structure if desired.

While the structure described above is especially suitable for bridges,similar structural arrangements can be used for the booms of derricks,power shovels and the like and to other beam-like elements which aresubjected to heavy loads. The lightness and strength of the structuralunits and freedom from frequent maintenance renders them superior tomany of the steel structures used heretofore for the purposes mentioned.Accordingly, it will be understood that the particular bridge decsribedin detail above is illustrative and is not considered to be limiting tothe scope of the following claims.

We claim:

1. A permanent composite bridge structure comprising a plurality ofhollow elongated beams extending lengthwise of said bridge structure inside by side and interconnected load transferring relationship, eachbeam being of triangular cross-section, each beam also having anupwardly disposed base and downwardly inclined sides and a downwardlydisposed corner, the sides of said beams comprising lightweight sheetmetal, corner members of thicker lightweight metal secured to thecorners of the beams, the downwardly inclined sides of one beam lying insubstantially parallel planes with the similarly disposed sides of theother beams, means connecting the downwardly disposed corners of thebeams, the corner members of a beam located adjacent both to theupwardly disposed base and the downwardly inclined sides thereof beingarranged in load transferring and interconnected relationship, a roadbedslab disposed upon the upwardly disposed bases of the beams, saidroadbed slab acting as the primary compression load bearing member inthe bridge structure, means including shear tie elements aflixed to thelast mentioned corner members of the beams and arranged transversely tothe longitudinal axis of the bridge structure, said shear tie elementsbeing embedded in the roadbed slab and acting to fully integrate theroa-dbed slab with the downwardly inclined sides of the beams wherebythe downwardly inclined sides Olf the beams and the means connecting thedownwardly disposed corners of the beams will act as the primary tensileload bearing elements of the bridge structure.

2. A composite bridge structure as set forth in claim 1 wherein saidshear tie elements are comprised of a plurality of Z-shaped members.

3. A composite bridge structure as set forth in claim 1 wherein saidlast mentioned corner members comprise a first corner member and asecond corner member disposed on opposite sides of each beam, said firstcorner member having a plurality of angularly disposed flanges and aridge formed in one of said flanges and the second corner membercomprising a plurality of anguliarly disposed flanges certain of whichmate with certain flanges on the first corner member of an adjacentbeam, one of the flanges of said second corner member having a groovewithin which the ridge on the first corner member of the said adjacentbeam is disposed, and means securing said first and second cornermembers together.

4. A composite bridge structure as set forth in claim 1 whereinstiflening members are secured to and extend transversely of thelongitudinal axis of the upwardly disposed bases and the downwardlyinclined sides of the beams.

5. A permanent composite bridge structure comprising in combination aplurality of hollow elongated beams extending lengthwise of said bridgestructure in side-by-side and interconnected load transferringrelationship, each beam being of triangular cross-section and each beamhaving an upwardly disposed base and downwardly inclined sides and adownwardly disposed corner, the sides of said beams comprisinglightweight sheet metal, corner members of thicker lightweight metalsecured to the corners of the beams, the downwardly inclined sides ofone beam lying in substantially parallel planes with the similarlydisposed sides of the other beams, means including sheets of lightweightmetal connecting the downwardly disposed corners of the beams, thecorner members of a beam located adjacent to both the upwardly disposedbase and the downwardly inclined sides thereof being arranged in loadtransferring and interconnected relationship, a roadbed slab disposedupon the upwardly disposed bases of the beams, said roadbed slab actingas the primary compression load bearing member in the composite bridgestructure, means including shear tie elements atfixed to the lastmentioned corner members of the beams and arranged transversely to thelongitudinal mtis of the bridge structure, said shear tie elements beingembedded in the roadbed slab and acting to 'fully integrate the roadbedslab with the downwardly inclined sides of the beams whereby thedownwardly inclined sides of the beams and the means including sheetsconnecting the downwardly disposed corners of the beam will act as theprimary tensile load bearing elements of the bridge structure.

6. A composite bridge structure as set forth in claim 5 wherein saidshear tie elements are comprised of a plurality of Z-shaped members.

7. A composite bridge structure as set forth in claim 5 wherein saidlast mentioned corner members comprise a first corner member and asecond corner member disposed on opposite sides of each beam, said firstcorner member having a plurality of angularly disposed flanges and abridge formed in one of said flanges and the second corner membercomprising a plurality of angularly disposed flanges certain of whichmate with certain flanges on the first corner member of an adjacentbeam, one of the flanges of said second corner member having a groovewithin which is disposed the ridge on the first corner member of thesaid adjacent beam, and means securing the said first and second cornermembers together.

8. A composite bridge structure as set forth in claim 5 whereinstiffening members are secured to and extend transversely of thelongitudinal axes of the upwardly disposed bases and the downwardlyinclined sides of the beams.

9. A structural unit for a bridge comprising a plurality of elongatedrelatively narrow load-bearing beams disposed in side-by-side andinterconnected load-transferring relationship, each beam being oftriangular cross section and forming a substantially continuoustriangular cell provided with an upwardly disposed base and downwardlyinclined sides, the plurality of beams being so arranged whereby oneside of each beam is in a substantially parallel plane with a similarlydisposed side of each other beam and with the lower apices of the beamsfacing in the same direction, the sides of each beam being formed of alightweight sheet metal, corner pieces secured to each corner of a beamand formed of thicker lightweight metal and extending lengthwise of eachbeam, means joining said lower apices together and disposedsubstantially parallel with the upwardly disposed bases of said beamswhich are also located opposite the lower apices thereof, saidlastmentioned means and the downwardly inclined sides of the beamsacting as the primary tensile load-bearing elements of the structuralunit, stiffening members secured to and extending transversely to thesides and upwardly disposed bases of the beams and means including sheartie members rigidly affixed to the corner pieces of the beams that arelocated adjacent both to said upwardly disposed bases and the downwardlyinclined sides of the beams, said shear tie members extending in adirection transverse to the longitudinal axis of the beams and beingadapted to become fully embedded within a road-bed slab when the slab ismounted on the upwardly disposed bases of the beams, whereby the saidslab can act as the primary compression load-bearing element of thebridge in which the structural unit is incorporated and saidlast-mentioned corner pieces comprising a first corner piece and asecond corner piece disposed on opposite sides of each beam, said firstcorner piece having a plurality of angularly disposed flanges and aridge formed in one of said flanges and the second corner piececomprising a plurality of angularly disposed flanges certain of whichmate with certain flanges on the first corner piece of an adjacent beam,one of the flanges of said second corner piece having a groove withinwhich the ridge on the first corner piece of the said adjacent beam isdisposed and means securing said first and second corner piecestogether.

10. A structural unit for a bridge comprising a plurality of elongatedrelatively narrow load-bearing beams disposed in side-by-side andinterconnected load-transferring relationship, each beam being oftriangular cross section and forming a substantially continuoustriangular cell provided with an upwardly disposed base and downwardlyinclined sides, the plurality of beams being so arranged whereby oneside of each beam is in a substan- .metal and extending lengthwise ofeach beam, means including lightweight sheet metal joining said lowerap-ices together and disposed substantially parallel with the upwardlydisposed bases of said beams which are also located opposite the lowerapices thereof, said last-mentioned means including lightweight sheetmetal and the downwardly inclined sides of the beams acting as theprimary tensile load-bearing elements of the structural unit, stiffeningmembers secured to and extending transversely to the sides and theupwardly disposed bases of the beams and means including shear tiemembers rigidly affixed to the corner pieces of the beams that arelocated adjacent both to said upwardly disposed bases and the downwardlyinclined sides of the beams, said shear tie member extending in adirection transverse to the longitudinal axis of the beams and beingadapted to become fully embedded within a roadbed slab when the slab ismounted on the upwardly disposed bases of the beams, whereby the saidslab can act as the primary compression load-bearing ele ment of theelement of the bridge in which the structural unit is incorporated, saidlast-mentioned corner pieces comprising a first corner piece and asecond corner piece disposed on opposite sides of each beam, said firstcorner piece having a plurality of angularly disposed flanges and aridge formed in one of said flanges, the second corner piece comprisinga plurality of angularly disposed flanges certain of which mate withcertain flanges on the first corner piece of an adjacent beam and one ofthe flanges of said second corner piece having a groove within which theridge on the first corner piece of the said adjacent beam is disposedand means securing said first and second corner pieces together.

1-1. A structural unit for a bridge comprising a plurality of elongatedrelatively narrow load-bearing beams disposed in side-by-side andinterconnected load-transferring relationship, each beam being oftriangular cross section and forming a substantially continuoustriangular cell provided with an upwardly disposed base and downwardlyinclined StldBS, the plurality of beams being so arranged whereby oneside of each beam is in a substantially parallel plane with a similarlydisposed side of each other beam and with the lower apices of the beamsfacing in the same direction, the sides of each beam being formed of alightweight sheet metal, corner pieces secured to each corner of thebeam and formed of thicker lightweight metal and extending lengthwise ofeach beam, means joining said lower apices together and disposedsubstantially parallel with the'upwardly disposed bases of said beamswhich are also located opposite the lower apiccs thereof, saidlast-mentioned means and the downwardly inclined sides of the beamsacting as the primary tensile load-bearing elements of the structuralunit, stiffening members secured to and extending transversely to thesides and the upwardly disposed bases of the beams and said cornerpieces including a first corner piece and a second corner piece disposedon opposite sides of each beam and adjacent both to the upwardlydisposed base and the downwardly inclined sides thereof, said firstcorner piece being provided with ridge means, and the second cornerpiece being provided with a recess means within which the ridge means onthe first cornerpiece of an adjacent beam is disposed and means securingsaid first and second corner pieces together.

12. A structural unit for a bridge comprising a plurality of elongatedrelatively narrow load-bearing beams disposed in side-by-side andinterconnected load-transferring relationship, each beam being oftriangular cross section and forming a substantially continuoustriangular cell provided with an upwardly disposed base and downwardlyinclined sides, the plurality of beams being so arranged whereby oneside ofcach beam is in i8, substantially parallel plane with a similarlydisposed side of each other beam and with the lower apices of the beamsfacing in the same direction, the sides of each beam being formed of alightweight sheet metal, corner pieces secured to each corner of a beamand formed of thicker lightweight metal and extending lengthwise of eachbeam, means joining said lower apices together and disposedsubstantially parallel with the upwardly disposed bases of said beamswhich are also located opposite the lower apices thereof, saidlast-mentioned means and the downwardly inclined sides of the beamsacting as the primary tensile loadbearing elements of the structuralunit, stiifening members secured to and extending transversely to thesides and the upwardly disposed bases of the beams, means includingshear tie members rigidly afiixed to the corner pieces of the beams thatare located adjacent both to said upwardly disposed bases and thedownwardly inclined sides of the beams, said shear tie members extendingin a direction transverse to the longitudinal axis of the beams andbeing adapted to become fully embedded within a roadbed slab when theslab is mounted on the upwardly disposed bases of the beams, whereby thesaid slab can act as the primary compression load-bearing element of 10the bridge in which the structural unit is incorporated 2,001,315Proctor May 14, 1935 and said last-mentioned corner pieces comprising afirst 2,116,033 Malone May 3, 1938 corner piece and a second cornerpiece disposed on oppo- 2,245,688 Krueger June 17, 1941 site sides ofeach beam, said first corner piece being pro- 2,910,016 Faverty Oct. 27,1959 vided with ridge means and the second corner piece being 52,926,928 Bennett Mar. 1, 1960 provided with a recess means Within whichthe ridge means on the first corner piece of an adjacent beam is FOREIGNPATENTS] disposed Iand means securing said first and second cor- 9 329Great Britain 1 9 Her pieces together- 1 574,761 France 1924 ReferencesCited in the file of this patent g if f j f UNITED STATES PATENTS E l"1,073,542 Stewart Sept. 16, 1913 OTHER RLFERENCE" 1,688,723 Lathlop Oct.23, 1928 15 Engineering News-Record, Jan. 30, 1958, page 22. 1,874,572Montgomery Feb. 17, 1930 Thofehrn, abstract of rapplication Serial No.291,581

1,913,342 Schaffert June 6, 1933 published Apr. 27, 1943, AFC.publication.

1. A PERMANENT COMPOSITE BRIDGE STRUCTURE COMPRISING A PLURALITY OFHOLLOW ELONGATED BEAMS EXTENDING LENGTHWISE OF SAID BRIDGE STRUCTURE INSIDE-BY-SIDE AND INTERCONNECTED LOAD TRANSFERRING RELATIONSHIP, EACHBEAM BEING OF TRIANGULAR CROSS-SECTION, EACH BEAM ALSO HAVING ANUPWARDLY DISPOSED BASE AND DOWNWARDLY INCLINED SIDES AND A DOWNWARDLYDISPOSED CORNER, THE SIDES OF SAID BEAMS COMPRISING LIGHTWEIGHT SHEETMETAL, CORNER MEMBERS OF THICKER LIGHTWEIGHT METAL SECURED TO THECORNERS OF THE BEAMS, THE DOWNWARDLY INCLINED SIDES OF ONE BEAM LYING INSUBSTANTIALLY PARALLEL PLANES WITH THE SIMILARLY DISPOSED SIDES OF THEOTHER BEAMS, MEANS CONNECTING THE DOWNWARDLY DISPOSED CORNERS OF THEBEAMS, THE CORNER MEMBERS OF A BEAM LOCATED ADJACENT BOTH TO THEUPWARDLY DISPOSED BASE AND THE DOWNWARDLY INCLINED SIDES THEREOF BEINGARRANGED IN LOAD TRANSFERRING AND INTERCONNECTED RELATIONSHIP, A ROADBEDSLAB DISPOSED UPON THE UPWARDLY DISPOSED BASES OF THE BEAMS, SAIDROADBED SLAB ACTNG AS THE PRIMARY COMPRESSION LOAD BEARING MEMBER IN THEBRIDGE STRUCTURE, MEANS INCLUDING SHEAR TIE ELEMENTS AFFIXED TO THE LASTMENTIONED CORNER MEMBERS OF THE BEAMS AND ARRANGED TRANSVERSELY TO THELONGITUDINAL AXIS OF THE BRIDGE STRUCTURE, SAID SHEAR TIE ELEMENTS BEINGEMBEDDED IN THE ROADBED SLAB AND ACTING TO FULLY INTEGRATE THE ROADBEDSLAB WITH THE DOWNWARDLY INCLINED SIDES OF THE BEAMS WHEREBY THEDOWNWARDLY INCLINED SIDES OF THE BEAMS AND THE MEANS CONNECTING THEDOWNWARDLY DISPOSED CORNERS OF THE BEAMS WILL ACT AS THE PRIMARY TENSILELOAD BEARING ELEMENTS OF THE BRIDGE STRUCTURE